Turbine rotor construction



We. 4 1936. c. R. S-ODERBERG TURBINE ROTOR CONSTRUCTION Filed May 31', 1954 WITNESSES. (5W5 Patented Feb. 4, 1936 UNITED STATES ,zatsi ATNT OFFICE Westinghense Electric .52 Manufacturing Company, East Pittsburgh, Pa, a corporation of Pennsylvania Application May 31, 1934, Serial No. 728,223

Claims.

My invention relates to turbine rotors or spindles, more particularly to those of the large type and it has for an object to provide apparatus of this character constructed and arranged to have low heat inertia with the material disposed to effectively resist centrifugal stresses. With turbines employing drum rotors, the rotor is ordinarily much more massive than the stator, and this results in axial expansion of the stator and rotor structures at different rates, rendering maintenance of axial clearances difficult. In accordance with the present invention, the rotor is modified so as to increase the heat absorbing surface thereof in order that expansion of the rotor and of the stator may occur approximately, or more nearly at, the same rate.

It is old in the art to provide hollow turbine rotors or spindles arranged to have steam circulated therethrough in order to reduce the time of heating; however, the wall thickness required to withstand the centrifugal stresses minimizes the effectiveness of this arrangement. In accordance with my invention, I provide a forged steel rotor including a hollow drum with spindle ends connected thereto, the drum being interiorly grooved so as to leave inwardly-extending flanges between the grooves, the flanges strengthening the blade-carrying drum and also making it possible to heat or cool the rotor rapidly. The flanges and grooves increase the surface area exposed to the medium circulating through the rotor with the result that transfer of heat occurs quickly, and uniformity of expansion and contraction of the rotor is secured by having it consist of portions of substantially uniform thickness, that is, the thickness of the wall between the bottom of each groove and the rotor surface is substantially the same as the flange thickness between adjacent grooves. A further object of my invention is to provide an apparatus having these advantageous features of construction and of operation.

To avoid excessive creep rates and consequent more rapid growth of the spindle diameter, it is necessary to reduce the average stress, particularly at those portions of the rotor subject to high temperatures. To meet this condition, and still retain the advantages of the drum construction, the forged steel rotor has ample radial thickness to avoid excessive stresses and internal grooves are provided to faclitate rapid heating and cooling. Accordingly, a further object of my invention is to provide a rotor of the drum type wherein the creep rate is reduced. and one which may be rapidly heated and cooled.

These and other objects are effected by my invention as will be apparent from the following description and claims taken in connection with the accompanying drawing, forming a part of this application, in which:

The single view illustrates a rotor incorporating my improvement.

Referring to the drawing more in detail, I show a rotor of the forged-steel drum type consisting of a hollow drum ID, a spindle end H integral with the high pressure end of the drum, and a spindle end I2 connected to the low pressure end of the drum. I show the spindle end having a spigot portion i3 fitting the hollow interior of the drum with a pressed fit and having a radial flange I4 abutting the low-pressure end of the drum and preferably secured to the latter by screws I5. Blades IS are carried by the drum. While I show the spindle end integral with the drum at the high pressure end, it is to be understood that the spindle end and the drum may be formed separately and secured together in any suitable manner.

The hollow, forged-steel rotor drum has passages l and i8 affording communication between the hollow interior and the exterior thereof, whereby elastic fluid may pass inside and outside of the rotor to secure rapid heating and cooling thereof.

The rotor drum is provided with a plurality of internal grooves 20 forming inwardly-extending flanges 2! arranged between the grooves. Not only do the grooves and the flanges increase the surface area exposed to the hollow interior of the rotor, but the flanges serve to increase the resistance of the rotor to centrifugal stresses. Substantial uniformity of heating and cooling is secured by having the thickness of the drum wall between the bottom of a groove 2!] and the external surface approximately the same as the thickness of a flange 2!, the approximate uniformity of thicknesses assuring substantially uniform conductivity of heat throughout the material of the rotor incident to heating and cooling.

The outlet passages it are preferably arranged at an intermediate point in the length of the drum so that discharging steam may have energy abstracted therefrom between that point and the exhaust end of the turbine. In this way, it is assured that the portion of the turbine subjected to the highest temperatures is rendered quickly responsive to changes in temperature while entailing a minimum energy loss on account of steam circulated through the hollow interior of the turbine, the steam being returned to the main turbine passage just as soon as this purpose is achieved for further expansion in the energyabstracting elements of the turbine. Furthermore, it will be seen that the passages l1 and 18 preferably extend through the drum Walls at bottoms of grooves at the high-pressure end and at a desired intermediate point.

From the foregoing, it will be apparent that I have devised a turbine rotor of the hollow forged steel drum type which may be made in relatively large sizes, which is capable of rapidly accommodating itself to large temperature changes, and which has the material of the drum so disposed that relatively low average stresses are encountered in operation.

While I have shown my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

What I claim is:

1. In an elastic-fluid turbine, a rotor of the drum type including a blade-carrying body comprised by a single steel forging having an axial bore and being of relatively large radial thickness; said rotor having means for circulating elastic fluid through the bore and said body having internal circumferential grooves opening into the bore; the external surface of the body, the internal surface of the bore and the groove surfaces providing for rapid and substantial uniformity of temperature changes of the body in consequence of exposure thereof to elastic fluid.

2. In an elastic-fluid turbine, a rotor of the drum type including a blade-carrying body comprised by a single cylindrical steel forging having a cylindrical axial bore and being of relatively large radial thickness; said rotor having means providing for the circulation of elastic fluid through the bore and said body having internal circumferential grooves opening into the bore and distributed therealong; the external surface of the drum, the internal surface of the bore and the groove surfaces providing for rapid and substantial uniformity of temperature changes of the body in consequence of exposure of such surfaces to elastic fluid.

3. In an elastic fluid turbine, a rotor of the drum type including an elongated cylindrical body comprised by a single steel forging and having a cylindrical bore, said rotor having means providing for the circulation of elastic fluid through the bore and said body having internal circumferential grooves distributed along the body and opening into the bore, the grooves being of such depth and so spaced that a substantially uniform thickness of material of the body is included between surfaces exposed to elastic fluid.

4. In a steam turbine suitable for operation at high temperatures, a rotor of the drum type including an elongated cylindrical body comprised by a single steel forging having an axial bore, the body having a radial thickness substantially greater than that normally required to withstand Working stresses in order to reduce the stress below a safe working stress sufficiently so as to reduce the creep rate of the body, said rotor having means providing for the circulation of steam through the bore and said body having internal circumferential grooves distributed therealong and opening into the bore, whereby, so far as change in temperature is concerned, the body is capable of changing with the rapidity of one of substantially less radial thickness.

5. The combination as claimed in claim 4 wherein the means for securing circulation through the bore includes a plurality of inlet and outlet ports communicating with the bore and extending through the body and the inlet ports being arranged at the high-pressure end of the body.

CARL R. SODERBERG. 

